1. Field of the Invention
The present invention relates to a spindle motor that is furnished with a dynamic pressure bearing, particularly, relates to a spindle motor that is suitably installed in a slim disc device or a laser beam printer for driving it.
2. Description of the Related Art
A spindle motor has been demanded for stability at high velocity revolution and excellent durability. In order to cope with these demanded characteristics, a spindle motor, which is furnished with a dynamic pressure bearing device that employs fluidic lubricant, is generalized in the market.
On the other hand, sliming in profile is also demanded for a disc device such as a hard disc drive and a laser beam printer. As a result, a spindle motor; which is furnished with a dynamic pressure bearing device and installed in such a disc device or a laser beam printer, is obliged to be slimed in profile as thin as possible.
In this connection, the Japanese publication of unexamined patent applications No. 2001-65552 disclosed a spindle motor, which was aimed to be slim in profile. According to the spindle motor disclosed in the Japanese publication No. 2001-65552, a thrust bearing section is disposed on an outer circumferential surface of a sleeve, that is, outside a radial bearing section. Traditionally, such a thrust bearing section has been disposed on an end portion of a shaft.
In a conventional spindle motor, a radial bearing section is provided on an inner circumferential surface of a sleeve.
Further, both axial side surfaces of a protrusion section, which protrudes in the radial direction like a flange, are made to be a pair of thrust bearing sections. It shall be understood that these surfaces for the radial and thrust bearing sections are necessary to be formed with an extremely high degree of accuracy.
On the contrary, it is necessary for the conventional spindle motor to be formed with two extra surfaces for thrust bearing sections on the sleeve, which is already provided with a surface for the radial bearing section, in a direction that is perpendicular to the surface for the radial bearing section.
Accordingly, there exists a possible problem of deforming one surface for one thrust bearing section or the surface for the radial bearing section due to overloading while processing to form the one surface for the one thrust bearing section and to form the other surface for the other thrust bearing section thereafter.
In case the deforming occurs, vertical or horizontal degree of accuracy among the surfaces for the thrust and radial bearing sections is deteriorated, and resulting in increasing eccentricity of a shaft while rotating. In some cases, a rotor may contact with a stator, and possibly resulting in disabling a spindle motor to rotate. Consequently, the spindle motor is degraded in reliability.
Further, dynamic pressure is made to be uneven, and resulting in causing a problem of shortening life of the bearing.
Furthermore, in case such a spindle motor is installed in a disc device so as to drive a disc, error possibly occurs when information is recorded on or reproduced from a disc for recording, and possibly resulting in a problem such that recording or reproducing information in high density is difficult.